Circuit to add and subtract two differential signals

ABSTRACT

An electrical circuit to add and subtract differential input signals may be implemented using distributed differential transmission lines having a length substantially equal to one quarter of a wavelength of the differential input signals according to an effective electrical permeability of the transmission line. Alternatively, the electrical circuit may be implemented with lumped reactive elements.

BACKGROUND OF THE INVENTION

An electrical circuit to simultaneously add and subtract twodifferential input signals may have different uses, such as, forexample, in radio frequency (RF) applications.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention are illustrated by way of example and notlimitation in the figures of the accompanying drawings, in which likereference numerals indicate corresponding, analogous or similarelements, and in which:

FIG. 1 shows an exemplary block diagram in accordance with someembodiments of the invention;

FIG. 2 shows an exemplary electrical circuit including reactive elementsin accordance with some embodiments of the invention;

FIG. 3 shows an alternate exemplary electrical circuit includingreactive elements in accordance with some embodiments of the invention;

FIG. 4 shows an exemplary electrical circuit including transmissionlines in accordance with some embodiments of the invention;

FIG. 5 shows an alternate exemplary electrical circuit includingtransmission lines in accordance with some embodiments of the invention;and

FIG. 6 is a simplified block-diagram illustration of an exemplarycommunication system, in accordance with some embodiments of the presentinvention;

It will be appreciated that for simplicity and clarity of illustration,elements shown in the figures have not necessarily been drawn to scale.For example, the dimensions of some of the elements may be exaggeratedrelative to other elements for clarity.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

In the following detailed description, numerous specific details are setforth in order to provide a thorough understanding of embodiments of theinvention. However it will be understood by those of ordinary skill inthe art that the embodiments of the invention may be practiced withoutthese specific details. In other instances, well-known methods,procedures, components and circuits have not been described in detail soas not to obscure the embodiments of the invention.

It should be understood that the present invention may be used in avariety of applications. Although the present invention is not limitedin this respect, the circuits disclosed herein may be used in manyapparatuses such as the transmitters and receivers of a radio system.Radio systems intended to be included within the scope of the presentinvention include, by way of example only, cellular radio telephonecommunication systems, wireless local area networks that meet theexisting 802.11a, b, g, and future high data-rate versions of the above,two-way radio communication systems, one-way pagers, two-way pagers,personal communication systems (PCS), Bluetooth wireless communicationsystems, Zigbee wireless communication systems and the like.

Types of cellular radiotelephone communication systems intended to bewithin the scope of the present invention include, although not limitedto, Direct Sequence-Code Division Multiple Access (DS-CDMA) cellularradiotelephone communication systems, Global System for MobileCommunucations (GSM) cellular radiotelephone systems, North AmericanDigital Cellular (NADC) cellular radiotelephone systems, Time DivisionMultiple Access (TDMA) systems, Extended-TDMA (E-TDMA) cellularradiotelephone systems, wideband CDMA (WCDMA), General Packet RadioService (GPRS) systems, Enhanced Data for GSM Evolution (EDGE) systems,3.5G and 4G systems.

FIG. 1 shows an exemplary block diagram including an electrical circuit2 in accordance with some embodiments of the invention. Exemplaryelectrical circuit 2 may include a differential sum/difference block 4,signal sources 6 and 8, and load elements 10 and 12. Differentialsum/difference block 2 may include terminals 14, 16, 18, 20, 22, 24, 26and 28.

Signal source 6 may have terminals 30 and 32, and may have an outputimpedance Z_(a) between terminals 30 and 32, as described in equation(1):Z _(a)=(a ₁ +ja ₂), a ₁≧0,  (1)where j denotes the square root of minus one, a₁ is the real componentof output impedance Z_(a) and a₂ is the imaginary component of outputimpedance Z_(a).

In addition, signal source 6 may generate a differential signal S_(A)(t)between terminals 30 and 32, having the general form described inEquation (2):S _(A)(t)=A _(A)(t)·e ^(j2πf) ^(A) ^((t)t+jθ) ^(A) ^((t))  (2)where A_(A)(t) is the amplitude, f_(A)(t) is the frequency and θ_(A)(t)is the initial phase of the differential signal S_(A)(t), and t is atime variable.

Signal source 8 may have terminals 34 and 36, and may have an outputimpedance Z_(b) between terminals 34 and 36, as described in equation(3):Z _(b)=(b ₁ +jb ₂), b ₁≧0,  (3)where b₁ is the real component of output impedance Z_(b) and b₂ is theimaginary component of output impedance Z_(b).

In addition, signal source 8 may generate a differential signal S_(B)(t)between terminals 34 and 36, having the general form described inEquation (4):S _(B)(t)=A _(B)(t)·e ^(j2πf) ^(B) ^((t)t+jθ) ^(B) ^((t))  (4)where A_(B)(t) is the amplitude, f_(B)(t) is the frequency and θ_(B)(t)is the initial phase of the differential signal S_(B)(t).

Load element 10 may have terminals 38 and 40, and may have an inputimpedance Z_(c) between terminals 38 and 40, as described in equation(5):Z _(c)=(c ₁ +jc ₂), c ₁≧0  (5)where c₁ is the real component of output impedance Z_(c) and c₂ is theimaginary component of output impedance Z_(c).

Similarly, load element 12 may have terminals 42 and 44, and may have aninput impedance Z_(d) between terminals 42 and 44, as described inequation (6):Z _(d)=(d ₁ +jd ₂), d ₁≧0,  (6)where d₁ is the real component of output impedance Z_(d) and d₂ is theimaginary component of output impedance Z_(d).

Terminals 14 and 16 of a first differential input port of differentialsum/difference block 2 may be connected to terminals 30 and 32,respectively. Terminals 18 and 20 of a first differential output port ofdifferential sum/difference block 2 may be connected to terminals 40 and38, respectively. Terminals 22 and 24 of a second differential outputport of differential sum/difference block 2 may be connected toterminals 42 and 44, respectively. Terminals 26 and 28 of a seconddifferential input port of differential sum/difference block 2 may beconnected to terminals 36 and 34, respectively.

Although the present invention is not limited in this respect, signalsources 4 and 6 may have substantially equal output impedances, as shownin equation (7):Z _(b) ≈Z _(a)=(a ₁ +ja ₂) a ₁≧0,  (7)and load elements 8 and 10 may have substantially equal inputimpedances, as shown in equation (8):Z _(d) ≈Z _(c)=(c ₁ +jc ₂) c ₁≧0.  (8)Furthermore, the frequency of differential signal S_(A)(t) may besubstantially equal to the frequency of differential signal S_(B)(t), asshown in equation (9):f _(A)(t)≈f _(B)(t).  (9)

Moreover, the output impedance of signal sources 6 and 8 may besubstantially active, as shown in equation (10):a ₁ >>|a ₂|,  (10)and the input impedance of load elements 10 and 12 may be substantiallyactive, as shown in equation (11):c ₁ >>|c ₂|.  (11)

Differential sum/difference block 4 may output a differential signalS_(C)(t) at terminals 20 and 18, that may be substantially proportionalto the sum of signals S_(A)(t) and S_(B)(t), as shown in equation (12):

$\begin{matrix}{{{S_{C}(t)} \approx {K_{1} \cdot \left\{ {{S_{A}(t)} + {S_{B}(t)}} \right\} \cdot {\mathbb{e}}^{j\frac{\pi}{2}\;\frac{f{(t)}}{f_{0}}}}},} & (12)\end{matrix}$where K₁ is a coefficient of proportionality, and f₀ is a centerfrequency of f_(A)(t).

Furthermore, differential sum/difference block 4 may output adifferential signal S_(D)(t) between terminals 22 and 24 that may besubstantially proportional to the difference between signals S_(A)(t),and S_(B)(t), as shown in equation (13):

$\begin{matrix}{{{S_{D}(t)} \approx {K_{2} \cdot \left\{ {{S_{A}(t)} - {S_{B}(t)}} \right\} \cdot {\mathbb{e}}^{j\frac{\pi}{2}\;\frac{f{(t)}}{f_{0}}}}},} & (13)\end{matrix}$where K₂ is a coefficient of proportionality.Consequently differential sum/difference block 4 may be considered asum-difference combiner.

FIG. 2 shows an exemplary differential sum/difference block 104 inaccordance with some embodiments of the invention. Differentialsum/difference block 104 may be implemented or partially implemented inan integrated circuit assembled on a printed circuit board 100. Thoseelements of differential sum/difference block 104 that are notimplemented in the integrated circuit (which may be all elements ofdifferential sum/difference block 104) may be implemented in thepackaging of the integrated circuit, as discrete components assembled onprinted circuit board 100, as part of printed circuit board 100, or anycombination thereof.

Differential sum/difference block 104 may include lumped reactiveelements 106, 108, 110, 112, 114, 116, 118 and 120, having physicaldimensions that are significantly smaller than the wavelength λ_(A)(t)that is associated with frequency f_(A)(t). (The wavelength λ_(A)(t) maybe the wavelength of a signal at frequency f_(A)(t) in a material havingan effective electrical permeability similar to that of a lumpedreactive element.) Reactive elements 106, 108, 110, 112, 114, 116, 118and 120 may have a substantially equal impedance Z_(e), as described inequation (14):Z _(e)=(e ₁ +je ₂), e ₁≧0  (14)where e₁ is the real component of impedance Z_(e) and e₂ is theimaginary component of impedance Z_(e).

Differential sum/difference block 104 may include lumped reactiveelements 122, 124, 126 and 128, having physical dimensions that aresignificantly smaller than the wavelength λ_(A)(t). Reactive elements122, 124, 126 and 128 may have a substantially equal impedance Z_(f), asdescribed in equation (15):Z _(f)=(f ₁ +jf ₂), f ₁≧0  (15)where f₁ is the real component of impedance Z_(f) and f₂ is theimaginary component of impedance Z_(f).

Reactive elements 106, 118 and 122 may be connected to terminal 14.

Reactive elements 108, 120 and 122 may be connected to terminal 16.

Reactive elements 116, 120 and 128 may be connected to terminal 18.

Reactive elements 114, 118 and 128 may be connected to terminal 20.

Reactive elements 106, 110 and 124 may be connected to terminal 22.

Reactive elements 108, 112 and 124 may be connected to terminal 24.

Reactive elements 110, 116 and 126 may be connected to terminal 26.

Reactive elements 112, 114 and 126 may be connected to terminal 28.

According to a first exemplary embodiment of the invention, reactiveelements 106, 108, 110, 112, 114, 116, 118 and 120 may havesubstantially inductive impedances, and reactive elements 122, 124, 126and 128 may have substantially capacitive impedances, as shown inequations (16) and (17) respectively:Z _(e)=(e ₁ +je ₂), e ₁≧0, e ₂≧0, e ₁ <<|e ₂|  (16)Z _(f)=(f ₁ +jf ₂) f ₁≧0, f ₂≦0, f ₁ <<|f ₂|  (17)Moreover, the impedance of reactive elements 106, 108, 110, 112, 114,116, 118 and 120 may be substantially twice as much as the impedance ofreactive elements 122, 124, 126 and 128, as shown in equation (18):e ₂≈2|f ₂|.  (18)

Furthermore, although the scope of the present invention is not limitedin this respect, the impedance of reactive elements 106, 108, 110, 112,114, 116, 118 and 120 may be related to the impedances of signal sources6 and 8 and to the impedances of load elements 10 and 12, as shown inequation (19):e ₂≈√{square root over (2a ₁ ·c ₁)}.  (19)Similarly, the impedance of reactive elements 122, 124, 126 and 128 maybe related to the impedances of signal sources 6 and 8 and to theimpedances of load elements 10 and 12, as shown in equation (20):

$\begin{matrix}{f_{2} \approx {- {\sqrt{\frac{a_{1} \cdot c_{1}}{2}}.}}} & (20)\end{matrix}$

Differential signal S_(C)(t) may be substantially proportional to thesum of S_(A)(t) and S_(B)(t), as shown in equation (12), anddifferential signal S_(D)(t) may be substantially proportional to thedifference between S_(A)(t) and S_(B)(t), as shown in equation (13).

According to a second exemplary embodiment of the invention, reactiveelements 106, 108, 110, 112, 114, 116, 118 and 120 may havesubstantially capacitive impedances, and reactive elements 122, 124, 126and 128 may have substantially inductive impedances, as shown inequations (21) and (22) respectively:Z _(e)=(e ₁ +je ₂), e ₁≧0, e ₂≦0, e ₁ <<|e ₂|  (21)Z _(f)=(f ₁ +jf ₂), f ₁≧0, f ₂≧0, f ₁ <<|f ₂|.  (22)The impedance of reactive elements 106, 108, 110, 112, 114, 116, 118 and120 may be substantially twice as much as the impedance of reactiveelements 122, 124, 126 and 128, as shown in equation (23):f ₂≈2|e ₂|.  (23)

Furthermore, although the scope of the present invention is not limitedin this respect, the impedance of refactive elements 106, 108, 110, 112,114, 116, 118 and 120 may be related to the impedances of signal sources6 and 8 and the impedances of load elements 10 and 12, as shown inequation (24):e ₂≈−√{square root over (2a ₁ ·c ₁)}.  (24)Similarly, the impedance of reactive elements 122, 124, 126 and 128 maybe related to the impedances of signal sources 6 and 8 and theimpedances of load elements 10 and 12, as shown in equation (25):f ₂≈2√{square root over (2a ₁ ·c ₁)}.  (25)

Differential signal S_(C)(t) may be substantially proportional to thesum of S_(A)(t) and S_(B)(t), as shown in equation (12), anddifferential signal S_(D)(t) may be substantially proportional to thedifference between S_(A)(t) and S_(B)(t), as shown in equation (13).

The second embodiment, described above, may be modified to includecenter taps 130, 132, 134 and 136 for reactive elements 122, 124, 126and 128, respectively. Center taps 130, 132, 134 and 136 may beoptionally connected to a supply or a supply return signal (not shown).

In both the first and second exemplary embodiments, a non-exhaustivelist of examples for the reactive elements having substantiallycapacitive impedances includes a surface mounted device (SMI) capacitorlocated on a printed circuit board (PCB), a SMD capacitor located on asubstrate of an integrated circuit (IC) device, a through-holecapacitor, a metal-insulator-metal (MIM) capacitor, a metal-oxidesemiconductor (MOS) capacitor, poly capacitor, and the like.

In both the first and second exemplary embodiments, a non-exhaustivelist of examples for the reactive elements having substantiallyinductive impedances includes a SMD inductor located on a PCB, a SMDinductor located on a substrate of an IC device, a through-holeinductor, a planar on-chip inductor, and the like.

In the case of substantially inductive reactive elements having centertaps, a non-exhaustive list of examples includes any combination of anSMI differential inductor located on a PCB, a SMD differential inductorlocated on a substrate of an IC device, a through-hole differentialinductor, a planar on-chip differential inductor with a center tap, andthe like.

FIG. 3 shows an alternate exemplary differential sum/difference block105 in accordance with some embodiments of the invention. Differentialsum/difference block 105 may be implemented or partially implemented inan integrated circuit assembled on a printed circuit board 101. Thoseelements of differential sum/difference block 105 that are notimplemented in the integrated circuit (which may be all elements ofdifferential sum/difference block 105) may be implemented in thepackaging of the integrated circuit, as discrete components assembled onprinted circuit board 101, as part of printed circuit board 101, or anycombination thereof.

Differential sum/difference block 105 may include lumped reactiveelements 106, 108, 110, 112, 114, 116, 118 and 120, as describedhereinabove with respect to FIG. 2. The physical dimensions andimpedances of reactive elements 106, 108, 110, 112, 114, 116, 118 and120 may be as described hereinabove with respect to FIG. 2. Moreover, asdescribed hereinabove with respect to FIG. 2, differentialsum/difference block 105 may include center taps 130, 132, 134 and 136for reactive elements 122, 124, 126 and 128, respectively. Center taps130, 132, 134 and 136 may be optionally connected to a supply or asupply return signal (not shown).

Reactive elements 108, 118 and 122 may be connected to terminal 14.

Reactive elements 106, 120 and 122 may be connected to terminal 16.

Reactive elements 116, 120 and 128 may be connected to terminal 18.

Reactive elements 114, 118 and 128 may be connected to terminal 20.

Reactive elements 106, 110 and 124 may be connected to terminal 22.

Reactive elements 108, 112 and 124 may be connected to terminal 24.

Reactive elements 112, 114 and 126 may be connected to terminal 26.

Reactive elements 110, 116 and 126 may be connected to terminal 28.

FIG. 4 shows an exemplary distributed differential sum/difference block204 in accordance with some embodiments of the invention. Differentialsum/difference block 204 may be implemented on a printed circuit board200 or any other suitable implementation.

Differential sum/difference block 204 may include distributeddifferential transmission lines 206, 208, 210 and 212, having physicaldimensions substantially equal to one quarter of the wavelength λ_(A)(t)(the wavelength λ_(A)(t) may be the wavelength of a signal at frequencyf_(A)(t) in a material having an effective electrical permeabilitysimilar to that of a transmission line), and having a substantiallyequal impedance Z_(h), as described in equation (26):Z _(h)=(h ₁ +jh ₂), h ₁≧0, h ₁ ≧≧|h ₂|  (26)where h₁ is the real component of impedance Z_(h) and h₂ is theimaginary component of impedance Z_(h).

Impedance Z_(h) may be related to the impedances of signal sources 4 and6 and to the impedances of load elements 8 and 10, as shown in equation(27):h ₁≈√{square root over (2a ₁ ·c ₁)}.  (27)

Distributed differential transmission line 206 may include a conductor214 and a conductor 216. Distributed differential transmission line 206may have terminals 218 and 220 connected to conductor 214, and may haveterminals 222 and 224 connected to conductor 216. Terminals 218 and 222may be associated with a first physical end of distributed differentialtransmission line 206, while terminals 220 and 224 may be associatedwith a second physical end of distributed differential transmission line206.

Distributed differential transmission line 208 may include a conductor226 and a conductor 228. Distributed differential transmission line 208may have terminals 230 and 232 connected to conductor 226, and may haveterminals 234 and 236 connected to conductor 228. Terminals 230 and 234may be associated with a first physical end of distributed differentialtransmission line 208, while terminals 232 and 236 may be associatedwith a second physical end of distributed differential transmission line208.

Distributed differential transmission line 210 may include a conductor238 and a conductor 240. Distributed differential transmission line 210may have terminals 242 and 244 connected to conductor 238, and may haveterminals 246 and 248 connected to conductor 240. Terminals 242 and 246may be associated with a first physical end of distributed differentialtransmission line 210, while terminals 244 and 248 may be associatedwith a second physical end of distributed differential transmission line210.

Distributed differential transmission line 212 may include a conductor250 and a conductor 252. Distributed differential transmission line 212may have terminals 256 and 258 connected to conductor 250, and may haveterminals 260 and 262 connected to conductor 252. Terminals 256 and 260may be associated with a first physical end of distributed differentialtransmission line 212, while terminals 258 and 262 may be associatedwith a second physical end of distributed differential transmission line212.

Terminals 218 and 244 may be connected to terminal 14.

Terminals 222 and 248 may be connected to terminal 16.

Terminals 224 and 258 may be connected to terminal 18.

Terminals 220 and 262 may be connected to terminal 20.

Terminals 234 and 242 may be connected to terminal 22.

Terminals 230 and 246 may be connected to terminal 24.

Terminals 236 and 256 may be connected to terminal 26.

Terminals 232 and 260 may be connected to terminal 28.

A non-exhaustive list of examples for distributed differentialtransmission lines 206, 208, 210 and 212 may include a differentialmicro-strip transmission line, a differential strip-line transmissionline, a differential waveguide, a differential coaxial cable, and thelike.

Differential signal S_(C)(t) may be substantially proportional to thesum of S_(A)(t) and S_(B)(t), as shown in equation (12), anddifferential signal S_(D)(t) may be substantially proportional to thedifference between S_(A)(t) and S_(B)(t), as shown in equation (13).

FIG. 5 shows an alternate exemplary differential sum/difference block205 in accordance with some embodiments of the invention. Differentialsum/difference block 205 may be implemented on a printed circuit board201 or any other suitable implementation.

Differential sum/difference block 205 may include distributeddifferential transmission lines 206, 208, 210 and 212, as describedhereinabove with respect to FIG. 4. The physical dimensions andimpedances of distributed differential transmission lines 206, 208, 210and 212 may be as described hereinabove with respect to FIG. 4.

Terminals 222 and 248 may be connected to terminal 14.

Terminals 218 and 244 may be connected to terminal 16.

Terminals 224 and 258 may be connected to terminal 18.

Terminals 220 and 262 may be connected to terminal 20.

Terminals 234 and 242 may be connected to terminal 22.

Terminals 230 and 246 may be connected to terminal 24.

Terminals 232 and 260 may be connected to terminal 26.

Terminals 236 and 256 may be connected to terminal 28.

FIG. 6 is a simplified block-diagram illustration of an exemplarycommunication system, in accordance with some embodiments of the presentinvention. A communication device 402 is able to communicate with acommunication device 404 over a communication channel 406. A transmitteraccording to embodiments of the present invention may be present incommunication device 402 only or in communication device 404 only or inboth communication devices 402 and 404. The following description isbased on the example of a transmitter according to one or another of theembodiments of the present invention present in communication device 402only, although the present invention is not limited in this respect.

Although the present invention is not limited in this respect, thecommunication system shown in FIG. 6 may be part of a cellularcommunication system, with one of communication devices 402, 404 being abase station and the other a mobile station or with both communicationdevices 402, 404 being mobile stations, a pager communication system, apersonal digital assistant and a server, etc. Communication devices 402and 404 may include antennas 408 and 410, respectively, which may be,for example, dipole antennas, loop antennas, shot antennas dualantennas, omni-directional antennas or any other suitable antennas.

Communication device 402 may include a transmitter 412 that may includea phase splitter 414, a differential sum/difference block 416 and apower amplifier 418. Phase splitter outphasing 414 may receive adifferential signal 420 that may contain information to be transmitted,and may output differential phase shifted signals 422 and 424 havingamplitudes substantially similar to the amplitude of signal 420.Differential phase shifted signal 424 may have a phase delay ofsubstantially 90° relative to differential phase shifted signal 422.

Differential sum/difference block 416 may receive differential phaseshifted signals 422 and 424 as inputs and may output a differential sumoutphased signal 426, and a differential difference outphased signal428.

Power amplifier 418 may receive differential sum outphased signal 426and may amplify it, using for example, a first power amplifying element(not shown). Similarly, power amplifier 418 may receive differentialdifference outphased signal 428 and may amplify it, using for example, asecond power amplifying element (not shown). Although the presentinvention is not limited in this respect, power amplifier 418 maycombine these amplified signals by means of, for example, atransmission-line-combiner with reactive shunt terminations, and mayoutput an RF signal 430 that may then be transmitted by antenna 408 overcommunication channel 406. Alternatively, the transmission-line-combinermay be replaced by a different combiner scheme, such as, for example,Hybrid BALUN or center-tap inductor.

Communication device 404 may include a receiver 432. Receiver 432 mayreceive a modulated data signal 434 from communication channel 406 viaantenna 410, and may, for example, extract the information contained insignal 434 by, for example, downconverting and demodulating signal 434.

It will be appreciated by persons of ordinary skill in the art thatcommunication devices 402 and 404, and in particular transmitter 412 andreceiver 432, may include additional components that are not shown inFIG. 4 so as not to obscure the description of embodiments of theinvention.

While certain features of the invention have been illustrated anddescribed herein, many modifications, substitutions, changes, andequivalents will now occur to those of ordinary skill in the art. It is,therefore, to be understood that the appended claims are intended tocover all such modifications and changes as fall within the spirit ofthe invention.

1. A combiner comprising: a circuit comprising a first group of sixreactive elements to couple two differential input ports to twodifferential output ports in a first manner; a second group of tworeactive elements to couple one of said two differential input ports toone of said two differential output ports in a second, different manner;and a third group of four reactive elements, each to couple a positiveterminal and a negative terminal of a respective one of said twodifferential input ports and said two differential output ports; whereinreactive elements of said first group and said second group havesubstantially equivalent inductive impedances and reactive elements ofsaid third group have substantially equivalent capacitive impedances. 2.The apparatus of claim 1, wherein said first manner is to couplepositive terminals to positive terminals and to couple negativeterminals to negative terminals, and said second manner is to couplepositive terminals to negative terminals.
 3. The apparatus of claim 1,wherein said first manner is to couple positive terminals to negativeterminals, and said second manner is to couple positive terminals topositive terminals and to couple negative terminals to negativeterminals.
 4. The apparatus of claim 1, wherein at least one of saidreactive elements is a discrete component.
 5. The apparatus of claim 1,wherein reactive elements of said first group and said second group havesubstantially equivalent capacitive impedances and reactive elements ofsaid third group have substantially equivalent inductive impedances. 6.The apparatus of claim 5, further comprising: a supply coupled to centertaps of said reactive elements of said third group.
 7. The apparatus ofclaim 5, further comprising: a supply return coupled to center taps ofsaid reactive elements of said third group.
 8. A communication devicecomprising: a dipole antenna; a power amplifier coupled to said dipoleantenna; and a combiner coupled to said power amplifier, wherein saidcombiner includes at least: a first group of six reactive elements tocouple two differential input ports to two differential output ports ina first manner; a second group of two reactive elements to couple one ofsaid two differential input ports to one of said two differential outputports in a second, different manner; and a third group of four reactiveelements, each to couple a positive terminal and a negative terminal ofa respective one of said two differential input ports and said twodifferential output ports.
 9. The communication device of claim 8,wherein said first manner is to couple positive terminals to positiveterminals and to couple negative terminals to negative terminals, andsaid second manner is to couple positive terminals to negativeterminals.
 10. The communication device of claim 8, wherein said firstmanner is to couple positive terminals to negative terminals, and saidsecond manner is to couple positive terminals to positive terminals andto couple negative terminals to negative terminals.
 11. Thecommunication device of claim 8, wherein reactive elements of said firstgroup and said second group have substantially equivalent inductiveimpedances and reactive elements of said third group have substantiallyequivalent capacitive impedances.
 12. The communication device of claim8, wherein reactive elements of said first group and said second grouphave substantially equivalent capacitive impedances and reactiveelements of said third group have substantially equivalent inductiveimpedances.
 13. A communication system comprising: a first communicationdevice; and a second communication device, said second communicationdevice including at least: a combiner including at least: a first groupof six reactive elements to couple two differential input ports to twodifferential output ports in a first manner; a second group of tworeactive elements to couple one of said two differential input ports toone of said two differential output ports in a second, different manner;and a third group of four reactive elements, each to couple a positiveterminal and a negative terminal of a respective one of said twodifferential input ports and said two differential output ports.
 14. Thecommunication device of claim 13, wherein said first manner is to couplepositive terminals to positive terminals and to couple negativeterminals to negative terminals, and said second manner is to couplepositive terminals to negative terminals.
 15. The communication deviceof claim 13, wherein said first manner is to couple positive terminalsto negative terminals, and said second manner is to couple positiveterminals to positive terminals and to couple negative terminals tonegative terminals.
 16. The communication device of claim 13, whereinreactive elements of said first group and said second group havesubstantially equivalent inductive impedances and reactive elements ofsaid third group have substantially equivalent capacitive impedances.17. The communication device of claim 13, wherein reactive elements ofsaid first group and said second group have substantially equivalentcapacitive impedances and reactive elements of said third group havesubstantially equivalent inductive impedances.